Gradient In Species Richness Research Articles

Imprints of latitude, host taxon, and decay stage on fungus‐associated arthropod communities

AbstractInteractions among fungi and insects involve hundreds of thousands of species. While insect communities on plants have formed some of the classic model systems in ecology, fungus‐based communities and the forces structuring them remain poorly studied by comparison. We characterize the arthropod communities associated with fruiting bodies of eight mycorrhizal basidiomycete fungus species from three different orders along a 1200‐km latitudinal gradient in northern Europe. We hypothesized that, matching the pattern seen for most insect taxa on plants, we would observe a general decrease in fungal‐associated species with latitude. Against this backdrop, we expected local communities to be structured by host identity and phylogeny, with more closely related fungal species sharing more similar communities of associated organisms. As a more unique dimension added by the ephemeral nature of fungal fruiting bodies, we expected further imprints generated by successional change, with younger fruiting bodies harboring communities different from older ones. Using DNA metabarcoding to identify arthropod communities from fungal fruiting bodies, we found that latitude left a clear imprint on fungus‐associated arthropod community composition, with host phylogeny and decay stage of fruiting bodies leaving lesser but still‐detectable effects. The main latitudinal imprint was on a high arthropod species turnover, with no detectable pattern in overall species richness. Overall, these findings paint a new picture of the drivers of fungus‐associated arthropod communities, suggesting that latitude will not affect how many arthropod species inhabit a fruiting body but, rather, what species will occur in it and at what relative abundances (as measured by sequence read counts). These patterns upset simplistic predictions regarding latitudinal gradients in species richness and in the strength of biotic interactions.

Elevational patterns of phylogenetic structure of angiosperms in a biodiversity hotspot in eastern Himalaya

AbstractAimsThe tropical niche conservatism (TNC) hypothesis and the out of the tropics (OTT) hypothesis propose mechanisms generating patterns of species diversity across warm‐to‐cold thermal gradients at large spatial scales. These two hypotheses both integrate ecological and biogeography‐related evolutionary factors, but they predict opposite patterns for phylogenetic structure. Mount Namjagbarwa possesses one of the longest elevational gradients for flowering plant diversity in the world. We aim to analyse the elevational patterns of the phylogenetic structure of flowering plants in this mountain, and investigate underlying causes for the emergence of the patterns.LocationMt. Namjagbarwa located at the eastern edge of the Himalaya.MethodsSpecies distribution data of Mt. Namjagbarwa were extracted from specimen records in online sources, literature, herbarium and our fieldwork. Bioclimatic data were extracted from the CHELSA database. Mt. Namjagbarwa was divided into 100‐m elevational belts, which were grouped into three elevation segments (100–2000 m, 2000–4000 m and 4000–5200 m) for data analysis. We calculated phylogenetic metrics for each belt. The relationships of phylogenetic metrics with elevation and climatic factors were analysed using generalized additive models and structural equation models.ResultsA typical hump‐shaped pattern of species richness was observed along the elevational gradient of Mt. Namjagbarwa. However, the phylogenetic structure showed a zig‐zag pattern with the three elevation segments, each of which has different formation mechanisms. Temperature tolerance played important roles throughout the entire elevational gradient in species richness and phylogenetic structure.Main conclusionsNeither TNC nor OTT alone can fully explain the patterns of floristic assembly of the entire elevational gradient of Mt. Namjagbarwa. OTT and TNC are better explanation for the patterns of low and middle elevations respectively. Potential mechanisms for species assembly of different elevation segments in Mt. Namjagbarwa region alternate between niche convergence and niche conservatism. The patterns observed in this study are likely to be common across the entire Himalaya. This is important for preserving the evolutionary potential of mountain biodiversity. However, more studies are needed to determine the underlying mechanisms generating the zig‐zag pattern of the phylogenetic structure in the Himalaya.

Niche partitioning in nitrogen uptake among subtropical tree species enhances biomass production

Nitrogen (N) is a main nutrient limiting plant growth in most terrestrial ecosystems, but so far it remains unknown which role plant N uptake plays for the positive relationship between species richness and productivity. An in situ15N labeling experiment was carried out by planting four subtropical tree species (i.e., Koelreuteria bipinnata, Lithocarpus glaber, Cyclobalanopsis myrsinaefolia and Castanopsis eyrei) in pots, at richness levels 1, 2 and 4 species per pot. Plant N uptake preference for inorganic N form of NO3− to NH4+ and organic N form of glycine, as well as biomass and plant functional traits was evaluated under different tree species richness level. Overall, pot biomass productivity increased with tree species richness. Biomass of the most productive species, K. bipinnata increased, but not at the expense of a decreased growth of the other species. In mixtures, the species shifted their preference for the inorganic N form, from NO3− to NH4+ or vice versa. The uptake preference for glycine remained stable along the species richness gradient. Plant N uptake was well correlated with numerous functional traits, both aboveground, such as height and shoot diameter, and belowground, such as root diameter and root length. We conclude that increased ecosystem biomass production with tree species richness could be largely explained by niche partitioning in N uptake among tree species. Our findings highlight that niche partitioning for N uptake should be a possible important mechanism maintaining species diversity and ecosystem production in subtropical forests.

Forest canopy resists plant invasions: a case study ofChromolaena odoratain Sal (Shorea robusta) forests of Nepal

AbstractInvasive alien species are a major threat to global biodiversity due to the tremendous ecological and economic damage they cause in forestry, agriculture, wetlands, and pastoral resources. Understanding the spatial pattern of invasive alien species and disentangling the biophysical drivers of invasion at the forest stand level is essential for managing forest ecosystems and the wider landscape. However, forest-level and species-specific information on Invasive Alien Plant Species (IAPS) abundance and their spatial extent are largely lacking. In this context, we analysed the cover of one of the world’s worst invasive plants,Chromolaena odorata, in Sal (Shorea robusta) forest in central Nepal. Vegetation was sampled in four community forests using 0.01 ha square quadrats, covering the forest edge to the interior.C. odoratacover, floral richness, tree density, forest canopy cover, shrub cover, tree basal area, and disturbances were measured in each plot. We also explored forest and IAPS management practices in community forests.C. odoratacover was negatively correlated with forest canopy cover, distance to the road, angle of slope, and shrub cover. Tree canopy cover had the largest effect onC. odoratacover. No pattern ofC. odoratacover was seen along native species richness gradients. In conclusion, forest canopy cover is the overriding biotic covariate suppressingC. odoratacover in Sal forests.

Depth-range distribution and diversity patterns of a polychaete (Annelida) community in the continental shelf of the Southern Gulf of Mexico

We tested the mid-domain effect to evaluate the bathymetric patterns of annelid polychaete species richness from the Southern Gulf of Mexico as a possible hypothesis to explain the species richness gradient, exploring the overlapping of species depth ranges towards the middle continental shelf. The bathymetric gradient of the number of species was estimated using the depth ranges of 259 polychaete species and the mid-domain effect was tested using a Monte Carlo simulation program at bands of 10 m depth. The carbonate (234 species) and the terrigenous (121 species) Gulf shelves showed clear differences in species richness which was characterized by a highly significant presence of polychaetes with short depth ranges (<10 m). The distribution of richness could be described as a cubic polynomial curve but the maximum values for all case studied (200, 181 and 84 species, for the whole study area, and the carbonate and terrigenous shelves, respectively) are strongly skewed to shallow waters (40 m). This is not consistent with the peak of diversity at 60–70 m predicted by the model. Therefore, the observed patterns cannot be reproduced by the mid-domain effect, suggesting the existence of non-random factors affecting the species richness gradients in the Gulf. We also found a gradient from west to east in species richness with increasing species richness in the carbonate shelf.

Ecological constraints on elevational gradients of bird species richness in Tajikistan

The avifauna in Tajikistan has been widely studied for the last century, but specific work on species richness pattern along elevation gradients in Tajikistan is rarely investigated. Here, we reported the first study of bird species richness (BSR) in the high-altitude mountain systems (Tien Shan and Pamir-Alay) of Tajikistan which are very sensitive to the recent climate changes. We aim to explore the relationship of BSR pattern with elevation gradient and to determine the potential drivers underlying the patterns. We collected occurrence data from field surveys, published articles, and open access websites to compile a list of bird species along elevational gradients across the whole country. The BSR was counted by 100 ​m elevational bands ranging from 294 ​m to 5146 ​m. The patterns of BSR were calculated separately for five groups: all breeding birds, Passeriformes, Non-Passeriformes, large elevational range species, and small elevational range species. We calculated ecological and climatic factors of planimetric area, mid-domain effect (MDE), habitat heterogeneity (HH), mean annual temperature (MAT), temperature annual range (TAR), annual precipitation (AP), normalized difference vegetation index (NDVI), human influence index (HII), and human disturbance (HD) in each elevational band. A combination of polynomial regression, Pearson's correlation, and general least squares model analyses were used to test the effects of these factors on the BSR. A unimodal distribution pattern with a peak at 750–1950 m was observed for all breeding birds. The similar pattern was explored for Passeriformes and Non-Passeriformes, while species with different elevational range sizes had different shapes and peak elevations. For all the breeding birds and Passeriformes, BSR was significantly related to spatial, climate and human influence factors, while BSR of Non-Passeriformes positively correlated with all the given factors. First, second and fourth range classes of birds were significantly correlated with human influence factors. Moreover, large-ranged species had positive correlations with the mid-domain effect and weakly with habitat heterogeneity. We found that area, MAT and AP were the main factors to explain the richness pattern of birds, and the species richness increases with these three factors increasing. Multiple factors such as area and climate explain 84% of the variation in richness. Bivariate and multiple regression analyses revealed a consistent influence of spatial and climate factors in shaping the richness pattern for nearly all bird groups.

Contamination Levels of Potentially Toxic Elements and Foraminiferal Distribution Patterns in Lagos Lagoon: A Correlation Analysis

The ecological response of benthic foraminifera to bioavailable Potentially Toxic Elements (PTEs) was evaluated in Lagos Lagoon (Nigeria). We sampled and analyzed PTEs across Lagos Lagoon with the aim to investigate the extent of contaminated sediments, to document their distribution, and to explore the relationship between PTE concentration and the spatial distribution, composition, abundance, and species richness of benthic foraminifera biotas. PTE’s recordings showed a wide range reflecting a diffuse contamination, where Contamination and Enrichment Factor suggest low to extremely polluted sediments. Findings of a previous survey of the benthic foraminifera inhabiting Lagos Lagoon revealed diverse assemblages of benthic taxa, species-specific distribution patterns, gradients of species richness and abundance, and a disjunct distribution of agglutinated and hyaline-perforate/porcelaneous taxa along a pronounced salinity gradient. Correlation matrix analysis shows that except for Selenium, all PTE total concentrations positively correlate with mud and Total Organic Carbon (TOC) and two of the most abundant agglutinated taxa, Ammotium salsum, and Trochammina sp. 1. Moreover, both species display significant positive correlations with CrF4-CoF2-F3-F4-total-CuF4-total-NiF3-F4-total-AlF4-total-FeF3-F4-total-ZnF3-F4-total. On the other hand, both foraminifers correlate negatively with PbF4-SeF3-Setotal. The overall significant positive correlation of these PTEs suggests that they behave as micronutrients when complexed with organic matter. No significant positive correlation with none of the PTEs in any fraction was found for neither species richness nor for the most abundant hyaline perforate species (Ammonia aoteana). Some PTE fractions were found to correlate either positively or negatively with individual species, suggesting that they function as either micronutrients and/or stressors. The resulting Contamination Factor of the PTE total concentrations shows that only a few sample sites can be classified as “moderately” polluted for chromium, zinc, and copper and that all sampled sites are classified as “highly polluted” for selenium. The highest concentrations for Cr, Cu, Ni, and Zn were found towards the industrialized western part, an area that is characterized by moderate to high diversity but low abundances.

Genetic and species-level biodiversity patterns are linked by demography and ecological opportunity.

The processes that give rise to species richness gradients are not well understood, but may be linked to resource-based limits on the number of species a region can support. Ecological limits placed on regional species richness should also affect population demography, suggesting that these processes could also generate genetic diversity gradients. If true, we might better understand how broad-scale biodiversity patterns are formed by identifying the common causes of genetic diversity and species richness. We develop a hypothetical framework based on the consequences of regional variation in ecological limits set by resource availability and heterogeneity to simultaneously explain spatial patterns of species richness and neutral genetic diversity. Repurposing raw genotypic data spanning 38 mammal species sampled across 801 sites in North America, we show that estimates of genome-wide genetic diversity and species richness share spatial structure. Notably, species richness hotspots tend to harbor lower levels of within-species genetic variation. A structural equation model encompassing eco-evolutionary processes related to resource availability, habitat heterogeneity, and contemporary human disturbance supports the spatial patterns we detect. These results suggest broad-scale patterns of species richness and genetic diversity could both partly be caused by intraspecific demographic and evolutionary processes acting simultaneously across species.

Impacts of vegetation properties and temperature characteristics on species richness patterns in drylands: Case study from Xinjiang

Energy availability at trophic and hydrologic level dominates species richness gradients by constraining food resources, and regulating population sizes and extinction rates. Remote sensing datasets have mapped vegetation productivities as a proxy for energy availability, for example, using Dynamic Habitat Indices (DHIs). Considering the sparse vegetation across drylands, we developed indices of Land surface temperature (ILST) based on daytime land surface temperature from Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS), which has three components: (1) annual mean temperature (LSTmean), (2) annual maximum temperature (LSTmax), and (3) standard deviation of temperature (LSTstd). We hypothesized that the temperature variables, such as ILST, would predict species richness better than productivity proxies across drylands. Thus, our objective was to determine how well they would predict the richness of plants, mammals and birds across the Xinjiang Uygur Autonomous Region. We calculated the DHIs and ILST from the MODIS vegetation and temperature products from 2001 to 2015. We found that: (1) ILST could capture more additive information compared with DHIs in terms of the relatively high variance explanation of species richness and high variable importance, and the combination of ILST and DHIs gave better predictions than single metrics for species richness patterns. (2) Plants and birds were more sensitive to temperature than vegetation productivity, probably due to physiological tolerance and evolutionary processes. (3) LSTstd was the most important variable affecting species richness, except on mammals. High LSTstd was related to more food resources and habitats, and low LSTstd represented extreme environment and environmental stress. Combined vegetation properties and temperature variabilities are good determinants of species richness, and should be carefully considered in future research.

Key roles for the freezing line and disturbance in driving the low plant species richness of temperate regions

AbstractAimAt the macroscale, climate strongly correlates with species richness gradients, resulting from differences in in‐situ diversification and dispersal. One historical explanation for the pattern is that regions spanning temperate climates contain few species because past disturbances have generated high extinction rates, and species from tropical regions are unable to easily colonize temperate regions. We test these postulates for Himalayan plants, which span subtropical to temperate climates over steep elevational gradients.LocationHimalaya.Time periodPresent day.Major taxa studiedAngiosperms.MethodsWe use a comprehensive survey of 31 floras to document the elevational and geographical distributions of native Himalayan plants, augmented by field studies of trees in both the east and west Himalaya. We use grade of membership models to cluster species according to locations shared and phylogenetic analysis to evaluate diversification rates.ResultsSpecies fall into four cohesive biotas, organized by climate. Points of turnover between biotas occur where the mean minimum temperature of the coldest month is approximately 0 °C (2,000–2,500 m), and at the point of occasional annual freezing (1,000–1,500 m); these boundaries run the length of the Himalaya. The patterns are retained when we consider whole clades rather than species. All plants (and the subsets trees, herbs and shrubs) belonging to the biota above the 2,000–2,500 m line have higher recent speciation rates than those lower down.Main conclusionsWe attribute the high rate of recent speciation in temperate climates to high rates of turnover, creating ecological and geographical opportunity. The high elevation biota has few species, but spans the largest area, implying species numbers are far from any carrying capacity, at least with respect to accumulation of allopatric forms. This study thus links climatic restrictions of clades to differences in diversification rates, and by inference species numbers.

Elevational range size patterns of vascular plants in the Himalaya contradict Rapoport's rule

Abstract Elevational range size patterns reflect ecological and evolutionary processes, but they are also affected by geometric constraints. The confounding effect of these constraints led to an ongoing controversy about the elevational Rapoport's rule, which postulates a positive association between the range size and elevation, and about the plausibility of the climate variability hypotheses as its causal explanation. Here we used an advanced null modelling approach to disentangle the interacting effects of geometric constraints and species richness gradients on the elevational range size of vascular plants. We collected extensive field data on elevational distribution for 728 vascular plant species occurring in the Ladakh region, Western Himalaya. We supplied these regional data with subcontinental elevational ranges extracted from the literature. Moreover, we used in situ measured temperatures to quantify temperature variability along an elevational gradient to test the climate variability hypothesis. Observed range size patterns were sensitive to methods used to quantify the average range size. Range truncation disproportionately affected regional ranges of low‐elevation species and resulted in spurious support of elevational Rapoport's rule. However, when the confounding effects of domain boundaries and richness gradient were controlled, our null models revealed only slight deviations from the random expectations of elevational range size patterns, contrasting with the prediction of the Rapoport's rule. In line with these findings, seasonal and diurnal temperature variability did not change with elevation. Synthesis. Geometric constraints combined with underlying species richness gradient create range size patterns seemingly supporting Rapoport's elevational rule. However, null models accounting for these effects indicate that the range size of vascular plants in the Himalayas does not increase with elevation. Given the universality of the geometric constraints and species richness gradient, our results suggest that these confounding factors must be controlled when testing Rapoport's rule. The null model approach described here provides an efficient tool to do that.

Vascular epiphytes contribute disproportionately to global centres of plant diversity

AbstractAimVascular epiphytes are ubiquitous components of wet tropical forests where they contribute substantially to local and regional plant diversity. While some basic epiphyte distribution patterns are relatively well studied, little effort has been made to understand the drivers responsible for constraining their global distribution. This study quantifies the substantial contribution of epiphytes to global gradients and centres of vascular plant diversity and explores whether epiphytes vary from terrestrial plants in relation to contemporary and historical environmental variables.LocationGlobal.Time periodPresent.Major taxa studiedTracheophyta.MethodsUsing a comprehensive epiphyte species list (EpiList 1.0), and distribution information for 27,850 epiphyte species derived from numerous literature sources, we describe the global biogeography of epiphytes. We use generalized linear mixed effects models to assess the relationship between epiphytic and terrestrial plant diversity, and contemporary and historical environmental predictors.ResultsEpiphytes substantially contribute to global centres of vascular plant diversity, accounting for up to 39% of the vascular flora in Neotropical regions. Epiphytes decrease in species numbers with increasing latitude at a rate three times faster than terrestrial plants, a trend that is driven mainly by the distribution of tropical forests and precipitation. Further, large regional differences emerge that are explained by several large endemic angiosperm families (e.g., Neotropical Bromeliaceae) that are absent in other tropical regions.Main conclusionsOur results show that epiphytes are disproportionately diverse in most global centres of plant diversity and play an important role in driving the global latitudinal diversity gradient for plants. The distribution of precipitation and tropical forest area emerge as major drivers of the latitudinal diversity gradient in epiphyte species richness. Finally, our findings demonstrate how epiphyte floras in different biogeographical realms are composed of different families and higher taxa, revealing an important signature of historical biogeography.

Soil Fungal Communities and Enzyme Activities along Local Tree Species Diversity Gradient in Subtropical Evergreen Forest

The majority of studies have found that an increase in tree species diversity can increase the productivity of forest stands thanks to complimentary effects with enhanced resource use efficiency or selection effects; however, it is unclear how tree species diversity affects the soil fungal community and enzyme activities in subtropical evergreen forests. In this study, we used soil high-throughput sequencing to investigate the soil fungal community structure and diversity in the central area of tree clusters in the gradient of tree species richness formed by four possible dominant tree species (Pinus massoniana Lamb., Choerospondias axillaris Roxb., Cyclobalanopsis glauca Thunb. and Lithocarpus glaber Thunb.) in subtropical evergreen broad-leaved forest. The results showed that soil organic carbon content and total nitrogen content were significantly higher in mixed tree clusters, and that soil fungal richness and diversity increased with the increase in tree species diversity (1–3 species). Soil acid phosphatase and urease activity were also enhanced with tree species diversity (p &lt; 0.05). The relative abundance of soil symbiotic fungi (ectomycorrhizal fungi) decreased, while the relative abundance of saprotrophic fungi increased. Redundancy analysis (RDA) revealed that soil acid phosphatase activity was the main factor affecting soil fungal communities and functional guilds, and that soil water content was the main driving force behind fungal trophic modes. In subtropical forests, changes in tree species diversity have altered the soil fungal community structure and trophic modes and functions, accelerating the decomposition of organic matter, increasing nutrient cycling, and perhaps also changing the nutrient absorption of trees.

Evolutionary drivers of the hump-shaped latitudinal gradient of benthic polychaete species richness along the Southeastern Pacific coast.

Latitudinal diversity gradients (LDG) and their explanatory factors are among the most challenging topics in macroecology and biogeography. Despite of its apparent generality, a growing body of evidence shows that ‘anomalous’ LDG (i.e., inverse or hump-shaped trends) are common among marine organisms along the Southeastern Pacific (SEP) coast. Here, we evaluate the shape of the LDG of marine benthic polychaetes and its underlying causes using a dataset of 643 species inhabiting the continental shelf (<200 m depth), using latitudinal bands with a spatial resolution of 0.5°, along the SEP (3–56° S). The explanatory value of six oceanographic (Sea Surface Temperature (SST), SST range, salinity, salinity range, primary productivity and shelf area), and one macroecological proxy (median latitudinal range of species) were assessed using a random forest model. The taxonomic structure was used to estimate the degree of niche conservatism of predictor variables and to estimate latitudinal trends in phylogenetic diversity, based on three indices (phylogenetic richness (PDSES), mean pairwise distance (MPDSES), and variation of pairwise distances (VPD)). The LDG exhibits a hump-shaped trend, with a maximum peak of species richness at ca. 42° S, declining towards northern and southern areas of SEP. The latitudinal pattern was also evident in local samples controlled by sampling effort. The random forest model had a high accuracy (pseudo-r2 = 0.95) and showed that the LDG could be explained by four variables (median latitudinal range, SST, salinity, and SST range), yet the functional relationship between species richness and these predictors was variable. A significant degree of phylogenetic conservatism was detected for the median latitudinal range and SST. PDSES increased toward the southern region, whereas VPD showed the opposite trend, both statistically significant. MPDSES has the same trend as PDSES, but it is not significant. Our results reinforce the idea that the south Chile fjord area, particularly the Chiloé region, was likely the evolutionary source of new species of marine polychaetes along SEP, creating a hotspot of diversity. Therefore, in the same way as the canonical LDG shows a decline in diversity while moving away from the tropics; on this case the decline occurs while moving away from Chiloé Island. These results, coupled with a strong phylogenetic signal of the main predictor variables suggest that processes operating mainly at evolutionary timescales govern the LDG.

Depth diversity gradients of macrophytes: Shape, drivers, and recent shifts.

Investigating diversity gradients helps to understand biodiversity drivers and threats. However, one diversity gradient is rarely assessed, namely how plant species distribute along the depth gradient of lakes. Here, we provide the first comprehensive characterization of depth diversity gradient (DDG) of alpha, beta, and gamma species richness of submerged macrophytes across multiple lakes. We characterize the DDG for additive richness components (alpha, beta, gamma), assess environmental drivers, and address temporal change over recent years. We take advantage of yet the largest dataset of macrophyte occurrence along lake depth (274 depth transects across 28 deep lakes) as well as of physiochemical measurements (12 deep lakes from 2006 to 2017 across Bavaria), provided publicly online by the Bavarian State Office for the Environment. We found a high variability in DDG shapes across the study lakes. The DDGs for alpha and gamma richness are predominantly hump‐shaped, while beta richness shows a decreasing DDG. Generalized additive mixed‐effect models indicate that the depth of the maximum richness (D max) is influenced by light quality, light quantity, and layering depth, whereas the respective maximum alpha richness within the depth gradient (R max) is significantly influenced by lake area only. Most observed DDGs seem generally stable over recent years. However, for single lakes we found significant linear trends for R max and D max going into different directions. The observed hump‐shaped DDGs agree with three competing hypotheses: the mid‐domain effect, the mean–disturbance hypothesis, and the mean–productivity hypothesis. The DDG amplitude seems driven by lake area (thus following known species–area relationships), whereas skewness depends on physiochemical factors, mainly water transparency and layering depth. Our results provide insights for conservation strategies and for mechanistic frameworks to disentangle competing explanatory hypotheses for the DDG.

Midpoint attractor models resolve the mid‐elevation peak in Himalayan plant species richness

The midpoint attractor (MPA) models of species richness integrate a unimodal environmental favourability gradient and neutral effects forced by geometric constraints and thus extend the ecologically neutral mid‐domain model. However, both alternative MPA algorithms assume that underlying environmental favourability peaks within the modelling domain. Here, we used elevational distribution data for 1054 plant species occurring in northwest Himalaya to explore species richness gradients and MPA performance in species groups defined by biogeography, taxonomy and life‐form. MPA models achieved an excellent fit, but the two MPA algorithms produced contrasting estimates of MPA location, especially for species groups with richness originating in lowlands. Therefore, we propose a modification of the MPA model accounting for the environmental favourability peak outside the study domain to reflect these situations. Biogeographic origin was more decisive for MPA location than taxonomic or life‐form classification, indicating relatively low climatic niche conservatism in plants.

Investigating elevational gradients of species richness in a Mediterranean plant hotspot using a published flora

The Apuan Alps are one of the most peculiar mountain chain in the Mediterranean, being very close to the coastline and reaching an elevation of almost 2000&nbsp;m. Based on published flora, we investigated the distribution of plant species richness along the whole elevational gradient of this chain considering: (i) all species, (ii) endemic versus alien species; and (iii) functional groups of species based on Raunkiær life forms (RLF). Generalized Linear Models (GLMs) were used to analyse richness patterns along the elevational gradient, and elevational richness models versus the area of the elevational belts were fitted to test the effect of surface area. Our results showed decreasing species richness with increasing elevation. In contrast, endemic species richness increased along the elevational gradient. Alien species were mainly distributed at low elevations, but this result should be taken with caution since we used historical data. Species life forms were not equally distributed along the elevation gradient: chamaephytes and hemicryptophytes were the richest groups at high elevations, while therophytes showed highest species richness at low elevations. Our findings suggest that in the Apuan Alps there is a major elevational gradient in species composition that could reflect plant evolutionary history. Furthermore, we highlight the key role of published floras as a relevant source of biodiversity data.

Plant species diversity affects plant nutrient pools by affecting plant biomass and nutrient concentrations in high-nitrogen ecosystems

Plant species diversity affects plant nutrient pools, however, previous studies have not considered plant nutrient concentrations and biomass simultaneously. In this study, we conducted an experimental system with 90 microcosms simulating constructed wetlands (CWs). Four species were selected to set up a plant species richness gradient (1, 2, 3, 4 species) and fifteen species compositions. The plant biomass, plant N, phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) concentrations and pools were analyzed. Results showed that, (1) plant species richness increased plant biomass, and the presence of Oenanthe javanicae increased while the presence of Reineckia carnea decreased plant biomass; (2) plant species richness only increased plant K and Mg concentrations of the communities and plant Mg concentration of the species, and the presence of O. Javanica increased while the presence of R. Japonicus decreased plant N and P concentrations of the communities; (3) plant species richness increased plant N, P, K, Ca, and Mg pools, and the presence of O. Javanica increased while the presence of R. Carnea decreased plant N, P, K, Ca and Mg pools; (4) the four-species mixture produced more biomass and nutrient pools than the corresponding highest specific species monocultures. In case the plant uptake can remove nutrients from CWs through harvesting, the results suggest that both nutrient concentrations and biomass must be considered when evaluating the accumulation of nutrients. Assembling plant communities with high species richness (four species) or certain species (such as O. Javanica) is recommended to remove more nutrients from CWs through harvesting.

Tree species richness promotes an early increase of stand structural complexity in young subtropical plantations

Abstract Forest structural complexity has been identified as an important driver for promoting simultaneously biodiversity across trophic levels and multiple ecosystem services. However, we still have a limited understanding of the processes that lead to structural complex stands and how they evolve over time. Using terrestrial laser scanning (TLS), we quantified a three‐dimensional (3D) stand structural complexity index (SSCI) in an experimental plantation with a long gradient of tree species richness (1–24 species). The plantation was established in 2009, and we made use of a multi‐temporal TLS dataset recorded during 2012–2019. We found a positive relationship between tree species richness and structural complexity. This relationship became stronger over time. Ten years after planting, SSCI was on average two‐fold higher in 16‐ and 24‐species mixtures than in monocultures. Furthermore, we demonstrate that tree species richness promotes 3D stand structural complexity indirectly by fostering a high vertical heterogeneity and thus greater spatial complementarity in canopy space. Synthesis and applications. Our findings indicate that tree species richness plays a crucial role in promoting stand structural complexity in young plantations, and this role becomes more important already during early stand development. Thus, afforestation measures would benefit from planting multiple native tree species to initiate structurally complex stands.

Imprints of tropical niche conservatism and historical dispersal in the radiation of Tyrannidae (Aves: Passeriformes)

AbstractSpeciation events occurring within biogeographic regions, and historical dispersal between regions influence diversity patterns observed in present-day assemblages. Such assessment has been often performed based on the phylogenetic structure of local assemblages. We underline some issues with that approach, and show that more reliable evaluation of historical events influencing present-day diversity can be achieved by combining phylogenetic diversity to an estimate of species assemblage age based on ancestral range estimation. We apply the new approach to test two concurrent hypotheses—Tropical Niche Conservatism (TNC) and Out of The Tropics (OTT)—which provide alternative explanations to species richness gradients, as possible explanations to higher species richness in tropical assemblages of Tyrannidae birds in relation to temperate ones across the American continent. Tropical assemblages tended to be older and to show higher phylogenetic diversity than temperate ones, suggesting that recent events of historical dispersal carried out by few lineages likely drove species assembly in younger temperate assemblages. This finding provides support to TNC as the most probable explanation to species richness variation in tyrannid assemblages across the Americas. Combining phylogenetic structure measures with a flexible assemblage age metric calculated from ancestral range estimation allows deeper understanding of current diversity gradients.